1. Field of the Invention
The present invention relates to an image processing system, image processing method therefor, and storage medium.
2. Description of the Related Art
A printing apparatus capable of color printing (e.g., color printer) receives, for example, RGB multi-valued data as input image data, internally executes color conversion processing from R, G, and B into C, M, Y, and K, and prints with C, M, Y, and K color materials (inks or toners).
Most printing apparatuses of this type have a calibration function to suppress variations of output colors owing to an individual difference of the output apparatus, environmental dependence, aging, and the like. In calibration, a calibration color chart is printed and its color is measured. At this time, if a color chart formed from primary colors which are not mixtures of ink colors is used, the number of printed patches is relatively small. Calibration using a color chart formed from primary colors consumes a small amount of consumables (e.g., sheets and inks), and takes a short time for printing and measurement. This calibration is therefore suitable when executed frequently. However, the main purpose of the calibration using a color chart formed from primary colors is to adjust the density and lightness of each ink, and the degree of freedom of adjustment is low.
Variation factors of the output color include not only variations of the printing apparatus itself, but also the difference between lots of ink for use and that between lots of printing media to be output. In many cases, a difference in tint arising from the difference between lots of ink or printing media cannot be corrected by the above-mentioned correction of primary colors, that is, calibration using a 1D-LUT. For example, when the tint of a cyan (C) ink changes to be bluish due to the lot difference, it cannot be corrected only using a cyan 1D-LUT. In this case, the mixing balance between cyan (C), magenta (M), and yellow (Y) inks needs to be adjusted to correct the tint using a 3D-LUT. When correcting the tint based on the 3D-LUT, a color profile needs to be generated and changed. Generating and changing a color profile will be expressed as generation of a color profile at once.
To generate a color profile, it is necessary to print many mixed color patches by combining a plurality of ink colors variously as a color chart for generating a color profile, and measure the color of the chart. Printing a color chart for a color profile consumes a large amount of consumables and takes a long time for printing and measurement.
Thus, it is not preferable to generate a color profile frequently. However, when a color profile is generated, a combination of output colors can be freely adjusted, so the degree of freedom of adjustment is high.
There has conventionally been known a technique of determining whether to execute calibration based on the allowance of the calibration precision set for a print job, and selectively executing calibration using a 1D-LUT or change of a profile by multi-dimensional correction (see Japanese Patent Laid-Open No. 2006-209407).
Correction of a color profile (correction by a multi-dimensional LUT) is effective to cope with all possible variations, that is, variations of the output apparatus, variations of ink, and variations of printing media and reproduce a stable tint. However, the color profile requires a large consumption amount of consumables and a long working time, as described above, puts a heavy burden on the user, and is not practical in operation.
To the contrary, calibration (correction by a 1D-LUT) can cope with only frequent variations, that is, variations of the output apparatus, but requires only a small consumption amount of consumables and a short working time and is practical in operation. However, the calibration cannot deal with variations of ink and printing media, as described above, and printing may be done with an improper tint.
According to the method disclosed in Japanese Patent Laid-Open No. 2006-209407, correction by a 1D-LUT and that by a multi-dimensional LUT are switched and executed. However, the switching is fixed in advance by the system or needs to be determined by the user. When the user is to make a determination, he has to select an appropriate correction method after analyzing a variation factor. This puts a heavy burden on the user.